This invention relates to lamp ballasts and to reactors for lighting and other applications that have magnetic cores made of amorphous metal.
Special circuitry is required for the starting and running of fluorescent and mercury lamps from an alternating current supply. These lamps have a negative resistance characteristic which must be compensated by ballasting impedance, and the ballast also supplies higher or peaked voltage for starting and a regulated current for running. It is desirable that the current through the lamp be flat topped to increase the life of the lamp. A high reactance transformer or reactor is needed to meet the requirements of a good ballast, and a capacitor can be added to realize a leading power factor on the supply circuit. Conventional magnetic ballasts are made from steel lamination punchings and include magnetic shunts and cutaways to cause saturation, and reactors are constructed from punchings and have a precisely controlled air gap. The present configurations substitute an amorphous metal wound core for these laminations.
Amorphous metal is also known as metallic glass and exists in many different compositions including a variety of magnetic alloys. Typical compositions include one or more of the transition elements such as iron or nickel and one or more of the glass formers such as boron or phosphorous. Metallic glasses are made from metal alloys that can be quenched rapidly without crystallization, and these solids have unusual and in some cases outstanding physical properties. They are mechanically stiff, strong and ductile, and the ferromagnetic types have very low coercive forces and high permeabilities. For power applications amorphous metal core material has great promise because of the combination of low cost (potentially) and low magnetic losses; the core loss in amorphous metal is about one-fourth the loss found in the best silicon steel. Other considerations relevant to electronic and power frequency components is given in "Potential of Amorphous Alloys for Application in Magnetic Devices", F. E. Luborsky et al, Journal of Applied Physics, Vol. 49, No. 3 (Part II), March 1978, pp. 1769-1774.
Amorphous metal ribbon with a thickness of 2 mils or less is prepared by rapid quenching of a stream of molten metal on a rotating chill cylinder; the thickness limitation is set by the rate of heat transfer through the already solidified material, which must be rapid enough that the last increment of material to solidify still avoids crystallization. This is several times thinner than currently used lamination materials, but this is advantageous from the point of view of eddy current losses. The resistivity of amorphous metal is three times that of currently used materials which would also decrease the eddy current loss. The main object of this invention is to produce lower cost magnetic ballasts and reactors with a higher power efficiency.